1. Field of the Invention
This invention relates to a consumable electrode for the production of alloys consisting of two or more active high melting point metals, and more particularly to a consumable electrode useful for the production of Nb-Ti alloys using vacuum arc melting techniques.
2. Description of the Prior Art
Nb-Ti alloys are conventionally produced by first forming a consumable electrode. The consumable electrode is arc or electron beam melted in a closed vessel in a vacuum or inert atmosphere to form an ingot. Inasmuch as the closed vessel is cooled by water or the like, the melted metal is rapidly cooled and gradually solidified in a lamellar manner in vertical direction, which makes it difficult to produce Nb-Ti alloys of homogeneous micro-structure without segregation.
Further, Ti has a melting point of 1668.degree. C. and specific gravity of 4.54, whereas Nb has a melting point of 2468.degree. C. and specific gravity of 8.57. This renders the production of Nb-Ti alloy ingots of homogenous microstructure without segregation by vacuum arc melting techniques using the conventional consumable electrode substantially impossible. In order to overcome the problem described above, many proposals have been made for the titanium-base consumable electrode which contains a high melting point alloying element in amount of several weight percent. However, these proposals are silent concerning the titanium base consumable electrode which contains the high-melting point alloying element at a level as high as about 50 wt. % or more.
The conventional consumable electrode for producing alloys consisting essentially of high-melting active metals is typically produced by thoroughly mixing the base metal and alloying elements and compacting the particles thereof. In the production of such a consumable electrode, when the difference in bulk density and particle size between the alloying element metal powder and the base metal powder is relatively small, it is possible to mix substantially uniformly both metal powders. However, in the consumable electrode for the production of Nb-Ti alloys, sponge titanium and niobium powder are highly different in particle size and bulk density, because sponge titanium has an average particle size of about 0.8-13 mm and bulk density of about 1.3, whereas niobium powder has an average particle size of about 0.07-1.0 mm and a bulk density of about 4.5. Thus, it is highly difficult to uniformly mix the sponge titanium and niobium powder together.
It is also known in the art to form a consumable electrode by alternately superposing a plurality of thin base metal sheets and a plurality of thin alloying element sheet on one another in the longitudinal direction. However, the consumable electrode of this type is disadvantageous in that the production of the thin metal sheets requires much cost and it is highly difficult to carry out welding in a chamber of an inert gas atmosphere.
A further consumable electrode known in the art is produced by throughly mixing matrix metal powder and alloying element metal powder to prepare a substantially homogeneous mixture thereof and subjecting the mixture to compression. Thereafter, the compressed mixture is placed at the center of matrix metal, to thereby form a compact. However, in the consumable electrode of this type, titanium powder used as a base metal in the electrode has a high oxygen content and expensive. Furthermore, the compacted mixture of matrix metal powder and alloying metal powder placed in the matrix metal makes it impossible to form the consumable electrode containing substantially equal amounts of niobium and titanium.